Add hovercard to policy parameter history chart with reference

[MaxGhenis]

For example, let's show where this $750 is from

https://policyengine.org/us/policy?focus=gov.hhs.medicaid.eligibility.categories.senior_or_disabled.income.limit.individual.CO&region=us&timePeriod=2023&baseline=2

[MaxGhenis]

This would also be a good opportunity to use our new hovercard style for the parameter one. e.g. this could have the reference with a link per the metadata:

like this does:

cc @zhiyanz

[anth-volk]

@MaxGhenis Could you provide more detail with regards to what you were looking for here?

[MaxGhenis]

parameters have reference metadata with titles and hrefs that we can surface

[anth-volk]

What I mean to say is, when you say "let's show where this $750 is from," do you mean the relevant piece of legislation, something variable-related, or something else?

[MaxGhenis]

What do you mean by variable-related? To start let's add the first reference in the parameter file.

[anth-volk]

I meant perhaps something computation-related, but I get what you're looking for now.